After conquering the data-communication and sensing markets, vertical-cavity surface-emitting lasers (VCSELs) are now playing a key role in imaging applications in smartphones and automotive contexts. In fact, among their "competitors", these lasers exhibit unique features in terms of power consumption, reliability, testability, packaging costs and array-oriented manufacturability, making them the ideal light source for portable applications. In order to export these advantages to the widest range of upcoming applications, the VCSEL community is exploring novel concepts and materials, aiming to move the emission from the consolidated 850nm wavelength towards mid-infrared and/or blue ranges. A criticality of VCSEL design is the injection of holes in the active region, which is controlled, in classical AlGaAs VCSELs, by an aperture obtained through wet oxidation processes.